Well known are abrasive wheel and spindle combinations of the type comprising a hub having axially-spaced inner and outer side flanges, abrasive material such as a multiplicity of abrasive-coated flexible strips, randomly woven abrasive coated material, or other abrasive material fastened between and projecting radially outwardly from between the side flanges, and a drive spindle coaxially and releasably attached to the abrasive wheel. The drive spindle can be coupled to a drive motor via a chuck, and the drive motor activated to rotate the spindle and abrasive wheel about their axes while the projecting abrasive material is pressed into engagement with a surface to abrade the surface.
There are many occasions on which it is necessary or desirable to change the abrasive wheel attached to the drive spindle such as when the abrasive in the wheel becomes worn or when it is desired to use a different grade of abrasive. Heretofore, however, the known means for releasably attaching the abrasive wheel to the spindle have not been as strong for their diameter, inexpensive, or as convenient to use as might be desired. One such means has included a machine screw or bolt having a head against the outer surface of the outer flange and extending through the hub and the inner flange so that a projecting threaded end portion of the bolt can releasably engage a threaded socket in an end of the drive spindle. Upon such engagement the end of the spindle seats in a socket along the outer surface of the inner flange, rotation of the drive spindle in the direction in which the spindle would further engage the threaded end portion will rotate the abrasive wheel with the spindle, and engagement of the bolt head and end of the spindle against the outer surfaces of the flanges will hold the flanges firmly together during use of the wheel. In some such attaching means the bolt is not fixed to the hub and detachment of the flap wheel requires the workman to release the bolt with a tool, such as a screwdriver, which tool may not always be readily available. In other such attachment means the bolt is fastened within the hub either by cementing it in place or by threadably engaging it with the inner flange. Such attachment prevents separation of the bolt from the hub and allows the abrasive wheel to be attached to the drive spindle without the use of tools by grabbing the abrasive wheel about its periphery and rotating it and the bolt with respect to the spindle, which spindle can typically be held by holding the chuck in which the spindle is engaged. This approach, however, requires that a bolt be supplied with each abrasive wheel, which, together with the necessity of positioning the bolt within the hub, significantly increases the cost of the abrasive wheel. Whether or not the bolt is attached within the hub, several threads on the projecting end portion of the bolt must be engaged with a corresponding number of threads in the spindle to ensure proper alignment of the abrasive wheel with the spindle, and engagement of these threads becomes so firm during use of the wheel that typically the chuck in which the spindle is engaged must be held with a tool before the abrasive wheel can be detached. Also, the thread on the bolt adjacent the inner flange both weakens and provides a stress concentration point in the bolt compared to an unthreaded shaft of the same diameter, which is undesirable in view of the stresses applied to the bolt at this point both by transverse forces applied to the abrasive wheel through the bolt and the high rotational speed at which the abrasive wheel is commonly used (e.g., 18,000 RPM for a 7.6 centimeter (3 inch) diameter wheel, which means that the wheel must commonly withstand testing at 50% overspeed or 27,000 R.P.M.).